1. Field of the Invention
The inventions disclosed and taught herein relate generally to filtration of drilling debris, and more specifically is related to systems and assemblies for removing contaminants from fluid streams above and near shale shakers proximate a drilling rig, particularly as associated with methods of drilling well bores in which gas or air is used as a drilling fluid for removing earth cuttings from the well bore, so as to prevent the uncontrolled release of the cuttings into the ambient environment.
2. Description of the Related Art
Within the drilling industry, drilling fluids, such as drilling mud, typically an admixture of an emulsion of water and base oil, clay, and various additives (such as weighting materials, emulsifiers, brines, pH-increasers, and viscosifiers), are pumped down through a drill string into a hydrocarbon-producing subterranean well. The drilling fluid is used to lubricate and cool the drill stem and bit, provide pressure support in the well, and transport cuttings from the working end of the drill bit to the surface. For example, drilling mud is typically pumped through a hollow drill string (pipe, drill collar, bit, etc.) down a wellbore and into a subterranean well, where it exits through holes in the drill bit. As the drilling fluid exits the drill string at the bottom through holes or jets in a drill bit and begins the return journey to the surface, the fluid picks up cuttings (rock bits) and other solids from the well and carries them upwardly away from the bit and out of the well via the annulus between the well and the drill string. Thus, while the drilling fluid performs a number of important functions, as it returns to the surface, it carries with it clays, chemical additives, hydrocarbon particles and water in an oil or water base.
Once the drilling fluid, or “mud”, is returned to the surface, equipment such as mud pits and shale shakers are used to remove and separate large amounts of coarse drilling cuttings from the drilling fluids so that the drilling fluids may be reused or recirculated within the well. More specifically, at the top of the well, the solids-laden drilling mud can be introduced to a shale shaker, a device which typically has a series of screens arranged in tiered or flat disposition with respect to each other. The screens catch and remove solids from the mud as the mud passes through them. If drilled solids are not removed from the mud used during the drilling operation, recirculation of the drilled solids can create viscosity and gel problems in the mud, as well as increasing wear in mud pumps and other mechanical equipment used for drilling. The cuttings are generally filtered out of the drilling fluid on a series of filters or screens provided within the shale shaker, which is essentially a vibrating screen where unwanted solids are removed, and the resultant cleaned drilling fluid separated and monitored. The drilling fluid that has passed through the shaker equipment is now clean of coarse debris and is ready to be cleaned via other processes prior to being ready for reuse.
On offshore drilling rigs, where area or space is a precious commodity, the equipment is typically located below the main work deck in an enclosed area. Drilling fluids typically contain a notable amount of volatile organic compounds and fugitive contaminants from the drilling process. This is because when passing through the drilling system, the drilling fluid is heated and hydrocarbon contaminants in the form of mist oil and oil vapor are generated at the shale shakers. For example, when drilling with oil-based drilling fluids or muds, the resultant return fluid has oil vapor concentrations of at least 300% above acceptable levels, as well as an oil “fog” in the area in front of and between the shale shakers. The design of the shale shakers themselves results in exposure of the potentially warm fluid to the workplace atmosphere of this otherwise typically enclosed process loop. Thus, workers in the drilling section of the drill facility, particularly in off-shore facilities, are exposed to elevated levels and concentrations of air pollutants generated by the drilling fluids. [Galea, K. S., et al., IOM Research Report TM/10/01, Apr. 10, 2010]. Because of this, the enclosed room is subject to forced ventilation to remove unpleasant and/or hazardous fumes. Depending on where the fumes are vented and the various and changing environmental conditions, the fumes may infiltrate other workspaces on the rig.
Apart from the expense and greater time requirements to drill the well, some circumstances simply do not permit the use of drilling mud or drilling fluids. For example, environmental, preservation and scenic regulations may not permit the discharge of a substantial amount of drilling mud into the adjoining earth formations, particularly if that discharge is likely to have a detrimental impact on water supplies within the earth formation or if the earth formation is adjacent to scenic and natural preserves which may be damaged by the influence of foreign substances penetrating into those formations. In situations like this, air drilling can be used.
Air drilling is a well drilling technique in which air or another gas or mixture of gases is used as the “drilling fluid” to remove the cuttings which are cut, broken, ground, eroded and otherwise separated from an earth formation by the drill bit as the drill bit cuts the well bore into the earth formation. Air, or a mixture of gases, is pressurized on the surface of the earth, forced down the center of a drill string of connected drilling pipes and discharged from the drill bit connected at the bottom end of the drill string. The drill bit cuts a circular opening which is slightly larger than the outside diameter of the drill string, thereby leaving a cylindrical space, called an annulus, between the outside of the drill string and the wall of the well bore. The cuttings which are separated from the earth formation are picked up and carried up the annulus by the flow of air discharged from the drill bit. Once at the surface, the cuttings are discharged into the ambient environment along with the air drilling fluid which carried the cuttings. The air drilling fluid continues to remove the cuttings from the bottom of the well bore, thereby maintaining the cutting efficiency of the drill bit in drilling through the earth formation.
A number of approaches to effectively filtering the debris and reducing the issues of debris and pollutants in the air surrounding shale shakers and similar devices have been described and implemented over the years. Primarily, these approaches involve the use of in-ceiling or ceiling adjacent filtering assemblies with complex ducting and fluid handling mechanics. While sometimes effective, the need for having to replace or clean physical filters, or the cost to repair the filtering system when it is damaged or blocked, leaves much to be desired with these current systems.
Although air drilling has advantages in avoiding some of the detrimental impacts from mud drilling in earth formations which are subject to loss of circulation, the disadvantage of air drilling is that the cuttings carried with the air to the surface of the earth are thereafter discharged directly into the ambient environment at the surface of the well with the air. This discharge may itself create an adverse environmental impact, because the cuttings are free to drift in the natural wind currents throughout the area surrounding the drilling site. In the instance of offshore drilling rigs, such a situation in a restricted environment can be dangerous to the operators near the discharge. Unlike mud drilling where the cuttings are readily separated from the drilling mud and stored in pits, containment ponds or other containers, the cuttings in the air drilling fluid are not believed to have been previously contained or otherwise separated from the discharged air. In those environmental circumstances where the cuttings cannot be discharged into the ambient environment, air drilling is not a preferred method of use.
It is with respect to these and other background factors and considerations that the present invention has resulted. The inventions disclosed and taught herein are directed to systems and apparatus for removing or minimizing air contaminants above or near a shale shaker, as well as methods of using and operating such a system, particularly contaminants or debris contained within a drilling fluid, including air drilling fluids.